The Development of the Northern European Fishery for North Atlantic Bluefin Tuna, Thunnus thynnus, during

Transcription

1 The Development of the Northern European Fishery for North Atlantic Bluefin Tuna, Thunnus thynnus, during Brian R. MacKenzie Technical University of Denmark & Aarhus University National Institute for Aquatic Resources Charlottenlund, Denmark

2 Acknowledgements -EU Network of Excellence on Marine Biodiv. & Ecosyst. Funct. -EU Network of Excellence on Ocean Ecosystem Dynamics Eur-oceans -HMAP ( -Danish climate change project

3 Objectives Describe development of bluefin tuna fishery in northeastern Europe. Estimate roles of fishery developments and ecosystem conditions on catch trends up to Kattegat L. Svendsen 1932.

4 Landings of Bluefin Tuna Thunnus thynnus in Northern Europe* Landings (tonnes) Intl. Danish Year * = Norwegian Sea, North Sea, Skagerrak, Kattegat, Øresund

5 Catch Development Before 1950 Landings (tonnes) Why did landings increase in early 1900s? -fishery related factors: increases in effort, technology, demand? -ecosystem and population factors? -changes in temperature, food supply, etc. -series of a few exceptionally strong yearclasses Year Intl. Danish

6 Methods -compile all existing data for presence of bluefin tuna in Northern European waters since presence = sightings, strandings, landings -individuals and schools -fishing industry information (effort, technology, processing) -compile time series of relevant ecosystem variables Data sources: -ICES -scientific papers, reports, books -commercial statistics, museum records, ichthyofaunal descriptions -photographic and video evidence MacKenzie & Myers 2007 Fish. Res.

7 Development of Fishery -many bluefin tuna were regularly seen esp. by herring fishermen -caught as bycatch in herring fisheries -offshore/open water (when hauling herring nets onboard) -coastal traps -some targetted fisheries with harpoons and harpoon-rifles MacKenzie & Myers 2007 Fish. Res.

8 Development of National Fisheries (ICES data: starts in 1927) Denmark Danish landings (t) German landings (t) Germany 100 Netherlands Dutch landings (t) 10 Norwegian landings (t) Norway France French landings (t) Swedish landings (t) Sweden MacKenzie & Myers 2007 Fish. Res.

9 Spatial Distribution of Bluefin Tuna Landings and Strandings before 1927 Le Grall 1927 J. du Conseil

10 A Day at Altona Fish Auction Hall, Germany, 1910 Photo: Brandenburg 2003; Sutton Verlag MacKenzie & Myers 2007 Fish. Res. -data not in ICES or ICCAT statistics

11 Development of National Fisheries pre-ices Norwegian landings (nos.) Danish landings at Skagen, DK (t) No. canneries Norway Denmark (1910: catch in 1 day) (1903: 1 stranding) German landings in North Sea (t) Swedish landings (t) Germany (1924: catch by 1 boat) 0 (1907: 1 stranding) Sweden France England : catch by 1 vessel French landings in North Sea (t) English sportfishery landings (nos.) MacKenzie & Myers 2007 Fish. Res.

12 Bluefin Tuna Sportfishery, Øresund, Denmark, 1949 Danmarks Radio Archives -viewable at

13 BluefinTuna School Sightings in North Sea Julian day Schools seen regularly by observers since schools observed near Dogger Bank during herring fishing Wolfe Murray 1932 J. du conseil

14 Prey Escape from Schools of Feeding Bluefin Tuna Svendsen, L garfish being attacked from below and jumping above water to escape

15 Commercial Bluefin Tuna Fishery, Kattegat, Denmark, 1949 Danmarks Radio Archives MacKenzie & Myers 2007 Fish. Res.

16 Tuna Presence and Multi-decadal Scale Temperature Variability North Sea SST during Summer Surface Temperature (North Sea) MacKenzie & Schiedek 2007 Glob. Ch. Biol. Bluefin tuna were present and abundant during: -cold periods ( ) -warm periods ( ). MacKenzie & Myers 2007 Fish. Res.

17 School Sightings & Temperature Summer SST North Sea SST during July-Aug-Sept First day Last day First day of sighting of tuna schools (Julian day) Last day of sighting of tuna schools (Julian day) presence/absence not related to interannual varations in regional SST Duration Duration of sightings of tuna schools (days) MacKenzie & Myers 2007 Fish. Res. North Sea SST, Hadley Ctr.

18 Tuna Presence and Multi-decadal Food Variability -herring were main prey of bluefin tuna in North and Norwegian Seas (Tiews 1964; 1978) Spawner biomass (1000s t) of Arct.-Norw. Herring Norweg. North Sea Spawner biomass (1000s t) of North Sea Herring Torsten & Østvedt 2000; ICES 2007 Bluefin tuna were present and abundant during: -low-food periods ( ) -high-food periods ( ).

19 Industrialisation of Northern European Bluefin Tuna Fisheries (1) -huge increase in effort (boats, gears, fishing skill) 500 Norwegian tuna fishing effort 400 No. of boats Hamre et al. 1966

20 Development of Fishing Methods L. Svendsen 1932 So. Kattegat, DK Hanson, B Norway L. Svendsen 1932 So. Kattegat, DK M. Tangen, 1999 Norway

21 Industrialisation of Northern European Bluefin Tuna Fisheries (2) -huge increase in technology and skill -harpoons, harpoon-rifles, rod-reel, handlines, hydraulically-operated purse seines -increase in demand and canneries (e. g., first Danish cannery built in 1920s; others followed in DK and Norway) -all these fishery-related changes lead to large increases in landings

22 Presence Before 1900 Tuna bones during Medieval (Enghoff 1999) 183 tuna caught in 1548 (Rørdam 1887) 1 fish caught 1545

23 Bluefin Tuna at Dutch Fish Market, 1545

24 Bluefin Tuna Fishing in Norway in 1760s Strøm, Hans Physical and Economic Description of Søndmør Tax District, Bergen Parish, Norway. Part 2

25 Bluefin Tuna Fishing in Norway in 1760s Documents written by professor and theologian Hans Strøm:

26 Bluefin Tuna Fishing in Norway in 1760s Every summer a large amount of tuna comes with the herring. One man could catch tuna per summer using a harpoon in the 1760s in Jørgenfjord, Norway. -H. Strøm 1766 H. Strøm 1788

27 Bluefin Tuna in Northern Europe Before 1900 All No. Europe Presence -based on fish fauna lists, fishery records, archaeological remains, etc present several decades and centuries in past MacKenzie, in prep.

28 Bluefin Tuna Near Copenhagen During the Stone Age (ca BC) Landskrona, Sweden (4000 BC; Eriksson & Magnell 2001) Amager Beach, Copenhagen (5800 BC) Enghoff et al Fish. Res.

29 Conclusions (Pre 1950) -bluefin tuna have been present in large numbers in northern European waters before onset of heavy fishing in 1950s-1960s -landings increased because of huge increases in effort & tech. -bluefin tuna are now extremely rare -gone from many people s memories (and expectations of which species comprise local fish community!) Next steps: -understand why collapse occurred in 1960s -understand why they have not (yet) returned

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31 Ecological and Fishing Influences on Presence of Bluefin Tuna in Northern European Waters Brian R. MacKenzie Technical University of Denmark & Aarhus University National Institute for Aquatic Resources DK-2920 Charlottenlund, Denmark

32 Talk Outline 1. Development of fisheries catch, effort, environmental data pre-1950s (MacKenzie and Myers 2007: Fish. Res.) 2. Current state why a decline and disappearance in 1960s -hypotheses 3. Prospects for recovery and reappearance

33 Hypotheses for Decline Hypothesis Temperature (too cold?) Food abundance not enough? Change in migration pattern Change in numbers of recruits migrating to region, due to -overexploitation of spawners and/or recruits -env. effects on recruitment processes -need to understand processes over large areas

34 Tuna Presence and Multi-decadal Scale Temperature Variability North Sea SST during Summer Surface Temperature (North Sea) MacKenzie & Schiedek 2007 Glob. Ch. Biol. SST during most of 1960s similar to earlier decades when BFT were also present -BFT also are good thermal-regulators and are usually seasonally present until SST < ~11-12 C -decline not likely due to low temperature MacKenzie & Myers 2007 Fish. Res.

35 Was Disappearance Related to Loss of Key Prey Species (Herring)? -herring collapsed in both Norwegian and North Seas in 1960s (mainly due to overfishing; Fiksen & Slotte 2002; Cushing 1995): Spawner biomass (1000s t) of Arct.-Norw. Herring Norweg. North Sea Spawner biomass (1000s t) of North Sea Herring Torsten & Østvedt 2000; ICES bluefin tuna may have altered migration pattern since main food supply was nearly eliminated MacKenzie et al., in prep.

36 Increase in Size Despite loss of prey, some big tuna still migrated here during 1960s-1980s. Decline accompanied by increase in size and age in Norwegian catches: -similar aging seen in Spanish catches (Pusineri et al. 2002) Fromentin & Powers 2005

37 Why Did Medium-Sized Tuna Stop Migrating to Northern Europe? Possible reasons: -young tuna changed their migration pattern (e. g., went somewhere else, stayed in Mediterranean, etc.) -reduced production of young tuna (low recruitment) due to fewer adults -lower survival of young tuna as juvenile exploitation increased (e. g., juvenile landings were 450,000/year in B. Biscay and Morocco during ; Cort & Nøttestad 2007)

38 Cause of Decline Main reason probably exploitation. Disappearance followed increasing and heavy exploitation of bluefin tuna and its prey in several areas: Species BFT BFT BFT Area Norwegian Sea North Sea Bay of Biscay LH Stage Mainly adults Mainly adults Mainly juveniles Herring Herring Norwegian Sea North Sea Juv. + adults Juv. + adults MacKenzie et al., in prep.

39 Reappearance Will they return? When?

40 Tuna Presence and Ecosystem Properties If presence depends on warm temperatures and high food abundance, then there should be lots of tuna in these waters: Surface Temperature (North Sea) Spawner biomass (1000s t) of Arct.-Norw. Herring Norweg. North Sea Spawner biomass (1000s t) of North Sea Herring MacKenzie et al. n prep.

41 Immigration of Southern Species to Northern European Waters -ocean warming is allowing many fish species to expand habitats to North and Norwegian Seas Science 308: (2005)

42 Southern Species Moving North Anchovy, survey data, Beare et al Swordfish Xiphias gladius; 66 kg Little Belt September, 2006 Gilthead seabream Sparus aurata Guldborgsund, western Baltic July 2007

43 Bluefin Tuna Reappearance? Bluefin tuna still very rare -1 caught as bycatch in Skagerrak in must consider other explanations related to population and fishing

44 Bluefin Tuna Catch Development Landings (tonnes) Total East. Atl. + Medit. Northern Europe (SD IIA, IIIA, IV) Danish (IIIA + IV) Year -large increase in reported landings in recent decades ICCAT 2006

45 Spawner Recruit Temporal Development Recruitment (age 1; 1000s) Rec. SSB Spawner biomass (1000s t) Recruits (age 1; 1000s) Spawner biomass (t) -decrease of spawner biomass is now limiting recruitment MacKenzie et al. in prep.

46 Reproductive Potential In other fish species and populations: -older, larger females and repeat spawners produce -more eggs/g, -better quality eggs -eggs over larger areas -eggs over longer periods of the year (Kjesbu, Marshall, Marteinsdottir, papers ) How has age structure of bluefin tuna changed relative to reproductive potential?

47 Population Demographics Proportion of age 8+ in stock proportion of old tuna in stock has declined, even from 1970 Repeat spawners as proportion of total spawners in stock proportion of repeat spawners has decreased

48 Trends in Population Demographics Reproductive potential of bluefin tuna has probably been reduced, for reasons in addition to the decrease in biomass of spawners. -quality of reproductive output may have decreased (assuming that BFT respond like other fish species?) -this will make recovery difficult and slower.

49 Landings of Juvenile Bluefin Tuna Catch of ages 1-3 (1000s) E. Atl + Med. B. Biscay & Atl. Morocco W. Atl Large numbers of 0-groups are also caught in E. Atl. and Med. but landings are unknown (ICCAT 2003, 2006). Prop. of ages 1-3 in total catch E. Atl + Med. W. Atl ICCAT 2006 ( ); Cort & Nøttestad 2007 ( )

50 Fishing Pattern in Eastern Atlantic -landings in Eastern Atlantic and Mediterranean dominated by immature fish -effects on past and future population dynamics needs to be investigated and quantified. -existing studies suggest exploitation of juveniles and adults is not sustainable (Fromentin & Fonteneau 2001) -many bluefin tuna not being given opportunity to reproduce

51 Conclusions (post 1950) Disappearance in 1960s not due to low temperatures. Disappearance mainly due to direct effects of fishing on -adult and juvenile bluefin tuna -prey (herring). Bluefin tuna has been present in these waters during cold and warm periods, and during food-rich and food-poor periods. If abundance associated with warm, food rich waters, there should now be lots of bluefin tuna in northern European waters. Recovery failure mainly due to continued high fishing on tuna adults and juveniles.

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